Radioisotope heat source boiler for power generators

ABSTRACT

The boiler essentially comprises a vessel of revolution having an external heat-insulating covering and a radioisotope source which is housed within the vessel. The source is constituted on the one hand by two blocks of revolution formed of material which is capable of providing a good biological shield. A peripheral recess is formed in each block in order to accommodate a tightlyfitting annular member, said member being constructed of material having a radioactive absorption coefficient which is higher than that of the blocks. The source is constituted on the other hand by a charge of radioelements formed by a series of clad radioactive plates arranged in stacks. The complete radioisotope source unit is immersed in a cooling liquid. The top end-wall of the boiler proper constitutes the hermetic cover of the vessel. A safety member which is welded to the upper block and to the cover ensures falling of the vessel and of the radioisotope source in the event of dangerous overheating.

July 25, 1972 RADIOISOTOPE HEAT SOURCE BOILER FOR POWER GENERATORS [72]Inventors: Michel Cohen, Paris; Pierre Lavigne, Grenoble; RobertSauvagnac, Antony, all of France [73] Assignee: Commissariat A LEnergieAtomlque,

Paris, France [22] Filed: June 9, 1970 [21] Appl. No.: 44,804

[30] Foreign Application Priority Data June 17, 1969 France ..6920l88[52] US. Cl ..126/344,176/26, 176/57 [51] Int. Cl ..G21c 15/18 [58]Field of Search ..176/57, 87, 26, 27; 126/344;

[56] References Cited 7 UNITED STATES PATENTS 3,171,791 3/1965 Wootton122/32 X 3,377,993 4/1968 7 Buck 122/32 Primary Examiner-Frederick L.Matteson Assistant Examiner-Harry B. Ramey Attorney-Cameron, Kerkam &Sutton [57] ABSTRACT The boiler essentially comprises a vessel ofrevolution having an external heat-insulating covering and aradioisotope source which is housed within the vessel. The source isconstituted on the one hand by two blocks of revolution formed ofmaterial which is capable of providing a good biological shield. Aperipheral recess is formed in'each block in order to accorrrmodate atightly-fitting annular member, said member being constructed ofmaterial having a radioactive absorption coefficient which is higherthan that of the blocks. The source is constituted on the other hand bya charge of radioelements formed by a series of clad radioactive platesarranged in stacks. The complete radioisotope source unit is immersed ina cooling liquid. The top end-wall of the boiler proper constitutes thehermetic cover of the vessel. A safety member which is welded to theupper block and to the cover ensures falling of the vessel and of theradioisotope source in the event of dangerous overheating.

10 Claims, 1 Drawing Figure RADIOISOTOPE HEAT SOURCE BOILER FOR POWERGENERATORS This invention relates to a radioisotope heat source boilerfor power generators and, in particular, for high-power electricgenerators.

Electric generators of the radioisotope source type can be dividedaccording to their power ratings into microgenerators, medium-powergenerators and high-power generators.

In particular, a known type of high-power electric generator comprises aconverter which operates on the Rankine cycle and is supplied by aboiler in which the fuel is a radioisotope source formed of cobalt-60pellets which have a double coating and are disposed at the center of aspherical tungsten shield.

This invention relates to a boiler for power generators and inparticular high-power electric generators, said boiler being intended tobe associated with a converter. The boiler essentially comprises avessel of revolution which is fabricated from stainless steel andprovided with an external heat-insulating covering formed of a laminatedstructure of layers having low conductivity and reflecting layers, aradioisotope source housed within said vessel and constituted on the onehand by two blocks of revolution fabricated from a material which iscapable of providing good biological protection and has good heatconductivity, said two blocks being placed at a small distance from eachother within said vessel so that the axes of revolution thereof shouldcoincide with the axis of said vessel and being each provided with aperipheral recess in which is tightly fitted an annular member formed ofmaterial having a radioactive absorption coefficient which is higherthan that of said blocks and on the other hand by a charge ofradioelements formed of a series of clad radioactive plates which arehoused in the space between said blocks and have the shape of very flatdiscs whose end faces are oriented at right angles to the axis ofrevolution of said blocks, said plates being arranged in stacks and eachstack being clamped between said blocks, the complete radioisotopesource being immersed in an organic cooling liquid having a boilingpoint which is higher than 250C, and a boiler proper whose top end-wallconstitutes the hermetic cover of said vessel, a safety member which isfusible at a given temperature and welded to the upper block and to saidcover being intended to ensure falling of said vessel and of saidradioisotope source in the event of dangerous overheating of saidsource.

The laminated structure which forms the heat insulating covering of saidvessel is composed, for example, of layers of glass wool and very thinaluminum sheets.

Advantageously, the two blocks of revolution are formed of copper andthe annular member which is adapted to fit in the peripheral recesses ofsaid blocks is formed of depleted urani- The plates which constitute thecharge of radioelements are advantageously formed of cobalt-60 and thecans of said plates are formed of stainless steel.

The organic cooling liquid in which the radioisotope source unit isimmersed is advantageously a diphenyl-diphenyloxide mixture in suitableproportions or alternatively liquid sodium or a liquid sodium-potassiummixture.

Further properties and advantages of the present invention will becomeapparent from the description which now follows below.

Reference will be made to the single accompanying FIGURE which shows byway of non-limitative example and in axial vertical cross-section aradioisotope source boiler according to the invention which is mountedon a power generator.

As appears from this figure, the boiler in accordance with the inventionis essentially constituted by a vessel 1 of revolution having aheat-insulating covering in the form of a laminated structure 2, aradioisotope source constituted on the one hand by two blocks 3 and 4 ofcopper (or tungsten) provided with peripheral recesses in which arefitted an annular member 5 of depleted uranium (or tungsten) and acopper ring l4 made up of two sections and on the other hand by a chargeof radioelements formed of a series of small plates 6 of cobalt-60 orstrontium, for example, said plates being clad with stainless steel andarranged in stacks which are clamped between the blocks 3 and 4. Theentire radioisotope source unit is immersed in a cooling liquid 7 suchas diphenyl-diphenyloxide, for example. The boiler 8 proper has a topend-wall 9 which serves as a hermetic cover for the vessel 1. A safetyplug 10 which is designed to melt at approximately 320C is welded to thevessel 1 and to the cover 9 of this latter and a safety member 15 whichis designed to melt in the vicinity of 400C is welded to the block 3 andto the cover 9.

The boiler unit according to the invention as hereinabove described andas shown in the figure is mounted beneath a power generator such as ahigh-power electric generator which does not specifically form part ofthe invention.

Said electric generator which is shown very diagrammatically in thedrawing comprises a converter formed of two stages containing differentorganic fluids which each flow in a Rankine cycle.

The boiler of the first stage of said converter (namely the stage whichhas the highest temperature) is the above-mentioned boiler 8. Thecondenser of said boiler (not shown) constitutes the boiler of thesecond stage. The condenser of said second stage (reference 11) isself-cooled by means of the surrounding air.

Provision is made for an emergency condenser (reference 12) of theself-cooled type which can be put into communication at 13 with the topportion of the vessel 1 in the event of an abnormal temperature rise.

The complete converter unit is supported on the ground by means ofstandards 16 which are embedded in concrete blocks 17, provision beingmade beneath the boiler in accordance with the invention for a pit 18which is covered with a glass plate 19. Finally, the two copper blocks 3and 4, the annular member 5 and the ring 14 are maintained clampedtogether by means of tie-rods 20.

The operation of the radioisotope source boiler in accordance with theinvention takes place as follows. By reason of the fact that the smallplates 6 are very flat discs and that the blocks 3 and 4 havesubstantially higher conductivity than the annular member 5, practicallythe entire quantity of heat given off by said small plates istransmitted by conduction into the frusto-conical portion of the copperblock 3 (as delimited in the figure by the chain-dotted line 21), thenby boiling of the organic liquid 7 and then by condensation on the topendwall 9 of the boiler 8 proper.

Only an extremely small proportion of the heat generated by the platesis transmitted through the annular member 5 of depleted uranium (ortungsten). Baffles (not shown in the figure) are provided between theblocks 3 and 4 and the member 5 in order to leave a clearance which doesnot present any hazard; by welding of lips, the combined assembly ofthese three elements is made impervious to any penetration of organicliquid 7 into the space which contains the charge of radioelements.

A number of different safety systems are provided in order to guardagainst any danger of an excessive temperature rise:

a. In the event of outage of the converter and a temperature rise to280C, for example, the emergency condenser 12 is put into communicationat 13 with the top portion of the vessel 1. Condensation of the vaporwhich is produced by the organic liquid 7 is then carried out in saidemergency condenser.

b. If the temperature attains 320C, for example, the plug 10 melts andatmospheric pressure is then established within the vessel 1. Thesurrounding air ensures sufficient cooling by reason of the fact thatthe maximum permissible temperature of the small plates of cobalt-60(reference 6) is of the order of 700C.

c. In the event of total failure of the converter, the ultimateemergency measure consists in detaching the complete assembly of vessel1 and heat insulation from the cover 9. To this end, if the temperatureattains 400C, for example, the

safety member melts, with the result that the block 3 and consequentlythe whole radioisotope source unit is detached from the cover 9 andfalls into the pit 18.

The radioisotope source boiler in accordance with the invention must beindestructible at the time of handling operations to which it may besubjected. To this end, impact resistance of the boiler in the event ofany accident condition arising during transportation is provided by aprotective cover or shell having an open structure which may be formedof expanded polystyrene, for example.

As is readily apparent, this invention has been described in theforegoing by way of explanation but not in any limiting sense and anydetail modifications may accordingly be contemplated without therebydeparting from its scope.

What we claim is l. A boiler for power generators and in particular forhighpower electric generators, wherein said boiler comprises a vessel ofrevolution which is fabricated from stainless steel and provided with anexternal heat-insulating covering formed of a laminated structure oflayers having low conductivity and reflecting layers, a radioisotopesource housed within said vessel and constituted on the one hand by twoblocks of revolution fabricated from a material which is capable ofproviding good biological protection and has good heat conductivity,said two blocks being placed at a small distance from each other withinsaid vessel so that the axes of revolution thereof should coincide withthe axis of said vessel and being each provided with a peripheral recessin which is tightly fitted an annular member formed of material having aradioactive absorption coefficient which is higher than that of saidblocks and on the other hand by a charge of radioelements formed of aseries of clad radioactive plates which are housed in the space betweensaid blocks and have the shape of very flat discs whose end faces areoriented at right angles to the axis of revolution of said blocks, saidplates being arranged in stacks and each stack being clamped betweensaid blocks, the complete radioisotope source being immersed in anorganic cooling liquid having a boiling point which is higher than 250C,and a boiler proper whose top end-wall constitutes the hermetic cover ofsaid vessel, a safety member which is fusible at a given temperature andwelded to the upper block and to said cover being intended to ensurefalling of said vessel and of said radioisotope source in the event ofdangerous overheating of said source.

2. A boiler in accordance with claim 1, wherein said laminated structureis composed of layers of glass wool and very thin aluminum sheets.

3. A boiler in accordance with claim I, wherein the two blocks ofrevolution are formed of copper.

4. A boiler in accordance with claim 1, wherein the two blocks ofrevolution are formed of tungsten.

5. A boiler in accordance with claim 1, wherein said annular member isformed of depleted uranium.

6. A boiler in accordance with claim 1, wherein said annular member isformed of tungsten.

7. A boiler in accordance with claim 1, wherein said plates are formedof cobalt-60.

8. A boiler in accordance with claim 1, wherein said plates are formedof strontium-90.

9. A boiler in accordance with claim 1, wherein said cooling liquid is adiphenyl-diphenyloxide mixture.

10. A boiler in accordance with claim I, wherein said cooling liquid isliquid sodium or a liquid sodium-potassium mixture.

IF I

1. A boiler for power generators and in particular for highpowerelectric generators, wherein said boiler comprises a vessel ofrevolution which is fabricated from stainless steel and provided with anexternal heat-insulating covering formed of a laminated structure oflayers having low conductivity and reflecting layers, a radioisotopesource housed within said vessel and constituted on the one hand by twoblocks of revolution fabricated from a material which is capable ofproviding good biological protection and has good heat conductivity,said two blocks being placed at a small distance from each other withinsaid vessel so that the axes of revolution thereof should coincide withthe axis of said vessel and being each provided with a peripheral recessin which is tightly fitted an annular member formed of material having aradioactive absorption coefficient which is higher than that of saidblocks and on the other hand by a charge of radioelements formed of aseries of clad radioactive plates which are housed in the space betweensaid blocks and have the shape of very flat discs whose end faces areoriented at right angles to the axis of revolution of said blocks, saidplates being arranged in stacks and each stack being clamped betweensaid blocks, the complete radioisotope source being immersed in anorganic cooling liquid having a boiling point which is highEr than250*C, and a boiler proper whose top end-wall constitutes the hermeticcover of said vessel, a safety member which is fusible at a giventemperature and welded to the upper block and to said cover beingintended to ensure falling of said vessel and of said radioisotopesource in the event of dangerous overheating of said source.
 2. A boilerin accordance with claim 1, wherein said laminated structure is composedof layers of glass wool and very thin aluminum sheets.
 3. A boiler inaccordance with claim 1, wherein the two blocks of revolution are formedof copper.
 4. A boiler in accordance with claim 1, wherein the twoblocks of revolution are formed of tungsten.
 5. A boiler in accordancewith claim 1, wherein said annular member is formed of depleted uranium.6. A boiler in accordance with claim 1, wherein said annular member isformed of tungsten.
 7. A boiler in accordance with claim 1, wherein saidplates are formed of cobalt-60.
 8. A boiler in accordance with claim 1,wherein said plates are formed of strontium-90.
 9. A boiler inaccordance with claim 1, wherein said cooling liquid is adiphenyl-diphenyloxide mixture.
 10. A boiler in accordance with claim 1,wherein said cooling liquid is liquid sodium or a liquidsodium-potassium mixture.